From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EB0A168 for ; Wed, 5 Jan 2022 22:47:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB84BC36AE9; Wed, 5 Jan 2022 22:47:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1641422847; bh=glZrEk8ggRtouJ5oR15cj7aPQIDczPe47sUNaQdinC8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JFFMfejQ3ftcyE/Nw8jDlZzlJxzO6tuF/QUglmOB7IdiYVKNBFL6kRHfiOIO8fTzj IGSYrjxeTtEOYQvTxbZ5mcu55CZtQR/tgK8yriNCiCpImJjY0t8en86pSd5X7SpxBc EDWVcFT/LeXM0yXuB2U+wuJdLi/66Xd3svQffDmTJ7kG4wrz8he0OEnie/WzpSxnAs EpT6amK/dJ5uvHJNbX1gL7u5/hTZR8XvvC/2TAn6q2HVLjITinoMbXdsvfUVaHpSNf H9O1uvANNivESMCaMYpMtQXYCf5aJ5Pub2qxz+pXgpAXcsvsiji5MFD6diNA6dGJXM fxTKUTf9yUt6Q== Date: Wed, 5 Jan 2022 14:47:27 -0800 From: "Darrick J. Wong" To: Dan Williams Cc: Shiyang Ruan , Linux Kernel Mailing List , linux-xfs , Linux NVDIMM , Linux MM , linux-fsdevel , david , Christoph Hellwig , Jane Chu Subject: Re: [PATCH v9 02/10] dax: Introduce holder for dax_device Message-ID: <20220105224727.GG398655@magnolia> References: <20211226143439.3985960-1-ruansy.fnst@fujitsu.com> <20211226143439.3985960-3-ruansy.fnst@fujitsu.com> <20220105181230.GC398655@magnolia> <20220105185626.GE398655@magnolia> Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jan 05, 2022 at 11:20:12AM -0800, Dan Williams wrote: > On Wed, Jan 5, 2022 at 10:56 AM Darrick J. Wong wrote: > > > > On Wed, Jan 05, 2022 at 10:23:08AM -0800, Dan Williams wrote: > > > On Wed, Jan 5, 2022 at 10:12 AM Darrick J. Wong wrote: > > > > > > > > On Sun, Dec 26, 2021 at 10:34:31PM +0800, Shiyang Ruan wrote: > > > > > To easily track filesystem from a pmem device, we introduce a holder for > > > > > dax_device structure, and also its operation. This holder is used to > > > > > remember who is using this dax_device: > > > > > - When it is the backend of a filesystem, the holder will be the > > > > > instance of this filesystem. > > > > > - When this pmem device is one of the targets in a mapped device, the > > > > > holder will be this mapped device. In this case, the mapped device > > > > > has its own dax_device and it will follow the first rule. So that we > > > > > can finally track to the filesystem we needed. > > > > > > > > > > The holder and holder_ops will be set when filesystem is being mounted, > > > > > or an target device is being activated. > > > > > > > > > > Signed-off-by: Shiyang Ruan > > > > > --- > > > > > drivers/dax/super.c | 62 +++++++++++++++++++++++++++++++++++++++++++++ > > > > > include/linux/dax.h | 29 +++++++++++++++++++++ > > > > > 2 files changed, 91 insertions(+) > > > > > > > > > > diff --git a/drivers/dax/super.c b/drivers/dax/super.c > > > > > index c46f56e33d40..94c51f2ee133 100644 > > > > > --- a/drivers/dax/super.c > > > > > +++ b/drivers/dax/super.c > > > > > @@ -20,15 +20,20 @@ > > > > > * @inode: core vfs > > > > > * @cdev: optional character interface for "device dax" > > > > > * @private: dax driver private data > > > > > + * @holder_data: holder of a dax_device: could be filesystem or mapped device > > > > > * @flags: state and boolean properties > > > > > + * @ops: operations for dax_device > > > > > + * @holder_ops: operations for the inner holder > > > > > */ > > > > > struct dax_device { > > > > > struct inode inode; > > > > > struct cdev cdev; > > > > > void *private; > > > > > struct percpu_rw_semaphore rwsem; > > > > > + void *holder_data; > > > > > unsigned long flags; > > > > > const struct dax_operations *ops; > > > > > + const struct dax_holder_operations *holder_ops; > > > > > }; > > > > > > > > > > static dev_t dax_devt; > > > > > @@ -192,6 +197,29 @@ int dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff, > > > > > } > > > > > EXPORT_SYMBOL_GPL(dax_zero_page_range); > > > > > > > > > > +int dax_holder_notify_failure(struct dax_device *dax_dev, u64 off, > > > > > + u64 len, int mf_flags) > > > > > +{ > > > > > + int rc; > > > > > + > > > > > + dax_read_lock(dax_dev); > > > > > + if (!dax_alive(dax_dev)) { > > > > > + rc = -ENXIO; > > > > > + goto out; > > > > > + } > > > > > + > > > > > + if (!dax_dev->holder_ops) { > > > > > + rc = -EOPNOTSUPP; > > > > > + goto out; > > > > > + } > > > > > + > > > > > + rc = dax_dev->holder_ops->notify_failure(dax_dev, off, len, mf_flags); > > > > > +out: > > > > > + dax_read_unlock(dax_dev); > > > > > + return rc; > > > > > +} > > > > > +EXPORT_SYMBOL_GPL(dax_holder_notify_failure); > > > > > + > > > > > #ifdef CONFIG_ARCH_HAS_PMEM_API > > > > > void arch_wb_cache_pmem(void *addr, size_t size); > > > > > void dax_flush(struct dax_device *dax_dev, void *addr, size_t size) > > > > > @@ -254,6 +282,10 @@ void kill_dax(struct dax_device *dax_dev) > > > > > return; > > > > > dax_write_lock(dax_dev); > > > > > clear_bit(DAXDEV_ALIVE, &dax_dev->flags); > > > > > + > > > > > + /* clear holder data */ > > > > > + dax_dev->holder_ops = NULL; > > > > > + dax_dev->holder_data = NULL; > > > > > dax_write_unlock(dax_dev); > > > > > } > > > > > EXPORT_SYMBOL_GPL(kill_dax); > > > > > @@ -401,6 +433,36 @@ void put_dax(struct dax_device *dax_dev) > > > > > } > > > > > EXPORT_SYMBOL_GPL(put_dax); > > > > > > > > > > +void dax_register_holder(struct dax_device *dax_dev, void *holder, > > > > > + const struct dax_holder_operations *ops) > > > > > +{ > > > > > + if (!dax_alive(dax_dev)) > > > > > + return; > > > > > + > > > > > + dax_dev->holder_data = holder; > > > > > + dax_dev->holder_ops = ops; > > > > > > > > Shouldn't this return an error code if the dax device is dead or if > > > > someone already registered a holder? I'm pretty sure XFS should not > > > > bind to a dax device if someone else already registered for it... > > > > > > Agree, yes. > > > > > > > > > > > ...unless you want to use a notifier chain for failure events so that > > > > there can be multiple consumers of dax failure events? > > > > > > No, I would hope not. It should be 1:1 holders to dax-devices. Similar > > > ownership semantics like bd_prepare_to_claim(). > > > > Does each partition on a pmem device still have its own dax_device? > > No, it never did... > > Just as before, each dax-device is still associated with a gendisk / > whole-block_device. The recent change is that instead of needing that > partition-block_device plumbed to convert a relative block number to > its absolute whole-block_device offset the filesystem now handles that > at iomap_begin() time. See: > > if (mapping_flags & IOMAP_DAX) > iomap->addr += target->bt_dax_part_off; > > ...in xfs_bmbt_to_iomap() (in -next). I.e. bdev_dax_pgoff() is gone > with the lead-in reworks. OH. Crap, Dan's right: XFS (pmem0p1): ddev dax = 0xffff88800304ed00 bdev = 0xffff8880480d6180 XFS (pmem0p2): ddev dax = 0xffff88800304ed00 bdev = 0xffff8880480d4380 Unless you're planning to remove partition support too, this patch needs to be reworked so that multiple filesystems in separate partitions can each call dax_register_holder to receive memory_failure notifications for their partition. /methinks this sharing is all a little scary... --D